Cancellation of pilot and traffic signals

ABSTRACT

A method for removing selected signals from a received signal prior to decoding begins by receiving communication signals from a transmitter over a CDMA air interface. The received communication signals are input to a traffic signal cancellation system for canceling unwanted traffic signals, thereby producing an output (O). The received communication signals are input to a pilot signal cancellation system for removing a global pilot signal, thereby producing an output (O add ). The output (O add ) of the pilot signal cancellation system is subtracted from the output (O) of the traffic signal cancellation system to provide a cancellation system output.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.11/234,768, filed on Sep. 23, 2005, which is a continuation of U.S.patent application Ser. No. 10/462,489, filed Jun. 16, 2003, now U.S.Pat. No. 6,950,411, which is a continuation of Ser. No. 10/266,408,filed Oct. 8, 2002, now U.S. Pat. No. 6,603,743, which is a continuationof U.S. patent application Ser. No. 09/175,174, filed Oct. 20, 1998, nowU.S. Pat. No. 6,498,784, which are incorporated by reference as if fullyset forth herein.

BACKGROUND OF THE INVENTION

The present invention relates generally to digital communications. Morespecifically, the invention relates to a system and method which cancelsthe global pilot signal and unwanted traffic signals from a receivedcode division multiple access signal thereby removing them asinterferers prior to decoding.

DESCRIPTION OF THE PRIOR ART

Advanced communication technology today makes use of a communicationtechnique in which data is transmitted with a broadened band bymodulating the data to be transmitted with a pseudo-noise (pn) signal.The technology is known as digital spread spectrum or code divisionmultiple access (CDMA). By transmitting a signal with a bandwidth muchgreater than the signal bandwidth, CDMA can transmit data without beingaffected by signal distortion or an interfering frequency in thetransmission path.

Shown in FIG. 1 is a simplified, single channel CDMA communicationsystem. A data signal with a given bandwidth is mixed with a spreadingcode generated by a pn sequence generator producing a digital spreadspectrum signal. The signal which carries data for a specific channel isknown as a traffic signal. Upon reception, the data is reproduced aftercorrelation with the same pn sequence used to transmit the data. Everyother signal within the transmission bandwidth appears as noise to thesignal being despread.

For timing synchronization with a receiver, an unmodulated trafficsignal known as a pilot signal is required for every transmitter. Thepilot signal allows respective receivers to synchronize with a giventransmitter, allowing despreading of a traffic signal at the receiver.

In a typical communication system, a base station communicates with aplurality of individual subscribers fixed or mobile. The base stationwhich transmits many signals, transmits a global pilot signal common tothe plurality of users serviced by that particular base station at ahigher power level. The global pilot is used for the initial acquisitionof an individual user and for the user to obtain signal-estimates forcoherent reception and for the combining of multipath components duringreception. Similarly, in a reverse direction, each subscriber transmitsa unique assigned pilot for communicating with the base station.

Only by having a matching pn sequence can a signal be decoded, however,all signals act as noise and interference. The global pilot and trafficsignals are noise to a traffic signal being despread. If the globalpilot and all unwanted traffic signals could be removed prior todespreading a desired signal, much of the overall noise would bereduced, decreasing the bit error rate and in turn, improving thesignal-to-noise ratio (SNR) of the despread signal.

Some attempts have been made to subtract the pilot signal from thereceived signal based on the relative strength of the pilot signal atthe receiver. However, the strength value is not an accuratecharacteristic for calculating interference due to the plurality ofreceived signals with different time delays caused by reflections due toterrain. Multipath propagation makes power level estimates unreliable.

There is a need to improve overall system performance by removingmultiple noise contributors from a signal prior to decoding.

SUMMARY OF THE INVENTION

A mobile user receiver having a cancellation system for removingselected signals from a traffic signal prior to decoding includes areceiver having a system input for receiving communication signals froma transmitter over an air interface. The system input is supplied to atraffic signal cancellation system for canceling unwanted trafficsignals. The system input is also supplied to a pilot signalcancellation system for removing a global pilot signal. The output ofthe pilot signal cancellation system is subtracted from the output ofthe traffic signal cancellation system to provide a cancellation systemoutput free from unwanted traffic signals and the global pilot signal.

A method for removing selected signals from a received signal prior todecoding begins by receiving communication signals from a transmitterover a CDMA air interface. The received communication signals are inputto a traffic signal cancellation system for canceling unwanted trafficsignals, thereby producing an output (O). The received communicationsignals are input to a pilot signal cancellation system for removing aglobal pilot signal, thereby producing an output (O_(add)). The output(O_(add)) of the pilot signal cancellation system is subtracted from theoutput (O) of the traffic signal cancellation system to provide acancellation system output.

A method for removing a global pilot code from a received signal beginsby despreading a global pilot code from a received signal. The strengthof the global pilot code is determined. The global pilot code iscross-correlated with a conjugate of a desired traffic code. The desiredtraffic code is despread from the received signal. The product of thestrength of the global pilot code and the cross-correlation result issubtracted from the despread desired traffic code.

A method for removing an unwanted traffic signal from a received signalbegins by despreading a desired traffic code from the received signal.At least one unwanted traffic code is despread from the received signal.The strength of the unwanted traffic code is determined and the unwantedtraffic data is determined from the despread unwanted traffic code. Thestrength of the unwanted traffic code and the unwanted traffic data aremultiplied. A conjugate of the desired traffic code and the unwantedtraffic code are cross-correlated. The result of the cross-correlationof a conjugate of the desired traffic code and the unwanted traffic codeis amplified according to the result of the multiplication of thestrength of the unwanted traffic code and the unwanted traffic data. Theresult of the amplification is subtracted from the despread desiredtraffic code.

A receiver having a system for canceling a pilot code from a receivedsignal includes a global pilot code despreader for despreading a globalpilot code from a received signal; means for generating a global pilotcode strength from the despread global pilot code; means for generatinga cross-correlation of a conjugate of a desired traffic code and theglobal pilot code; a mixer for mixing a global pilot code strength andthe output of the cross-correlation of the conjugate of the desiredtraffic code and the global pilot code; a desired traffic codedespreader for despreading a desired traffic code from the receivedsignal; and a summer for summing the output of the mixer and the outputof the desired traffic code despreader.

A receiver having a system for removing unwanted traffic signals from areceived signal prior to decoding includes a desired traffic codedespreader for despreading a desired traffic code from a receivedsignal; at least one unwanted traffic code canceller; and a summer forsumming the despread desired traffic code and the output of unwantedtraffic code canceller. Each unwanted traffic code canceller includes anunwanted traffic code despreader for despreading an unwanted trafficcode from the received signal; means for generating an unwanted trafficcode strength from the despread unwanted traffic code and fordetermining unwanted traffic data; a multiplier for multiplying theunwanted traffic data and the unwanted traffic code strength; across-correlator for cross-correlation of a conjugate of a desiredtraffic code and the unwanted traffic code; and a variable amplifier foramplifying the result of cross-correlation of a conjugate of a desiredtraffic code and the unwanted traffic code according to the result ofthe multiplication of the unwanted traffic data and the unwanted trafficcode strength.

A receiver having a means for canceling selected signals from a receivedsignal over a CDMA air interface includes an unwanted signal cancellerfor subtracting an unwanted traffic signal from a received signal and apilot signal canceller for subtracting a pilot signal from a receivedsignal.

The present invention reduces the contributive noise effects of theglobal pilot signal and unwanted traffic signals transmitted in a spreadspectrum communication system. The present invention effectively cancelsthe global pilot and unwanted traffic signal(s) from a desired trafficsignal at a receiver prior to decoding. The resulting signal has anincreased signal-to-noise ratio.

Accordingly, it is an object of the present invention to provide a codedivision multiple access communication system receiver which reduces thecontributive noise effects from the pilot and active, unwanted trafficsignals.

It is another object of the present invention to improve the desiredtraffic signal SNR by eliminating the noise effects of the global pilotand active traffic signals.

Other objects and advantages of the system and method will becomeapparent to those skilled in the art of advanced telecommunicationsafter reading the detailed description of the preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of a prior art, CDMA communicationsystem.

FIG. 2A is a detailed block diagram of a B-CDMA™ communication system.

FIG. 2B is a detailed system diagram of a complex number multiplier.

FIG. 3A is a plot of an in-phase bit stream.

FIG. 3B is a plot of a quadrature bit stream.

FIG. 3C is a plot of a pseudo-noise (pn) bit sequence.

FIG. 4 is a block diagram of a global pilot signal cancellation systemaccording to the present invention.

FIG. 5 is a block diagram of an unwanted traffic signal(s) cancellationsystem according to the present invention.

FIG. 6 is a diagram of a received symbol p_(o) on the QPSK constellationshowing a hard decision.

FIG. 7 is a block diagram of a combined pilot and unwanted trafficsignal cancellation system according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments will be described with reference to thedrawing figures where like numerals represent like elements throughout.

A B-CDMA™ communication system 17 as shown in FIG. 2 includes atransmitter 19 and a receiver 21, which may reside in either a basestation or a mobile user receiver. The transmitter 19 includes a signalprocessor 23 which encodes voice and nonvoice signals 25 into data atvarious bit rates.

By way of background, two steps are involved in the generation of atransmitted signal in a multiple access environment. First, the inputdata which can be considered a bi-phase modulated signal is encodedusing forward error-correcting coding (FEC) 27. One signal is designatedthe in-phase channel I 33 x. The other signal is designated thequadrature channel Q 33 y. Bi-phase modulated I and Q signals areusually referred to as quadrature phase shift keying (QPSK).

In the second step, the two bi-phase modulated data or symbols 33 x, 33y are spread with a complex, pseudo-noise (pn) sequence 35I, 35Q using acomplex number multiplier 39. The operation of a complex numbermultiplier 39 is shown in FIG. 2B and is well understood in the art. Thespreading operation can be represented as:(x+jy)×(I+jQ)=(xI−yQ)+j(xQ+yI)=a+jb.  Equation (1)

A complex number is in the form a+jb, where a and b are real numbers andj²=−1. Referring back to FIG. 2 a, the resulting I 37 a and Q 37 bspread signals are combined 45 a, 45 b with other spread signals(channels) having different spreading codes, multiplied (mixed) with acarrier signal 43, and transmitted 47. The transmission 47 may contain aplurality of individual signals.

The receiver 21 includes a demodulator 49 a, 49 b which mixes down thetransmitted broadband signal 47 with the transmitting carrier 43 into anintermediate carrier frequency 51 a, 51 b. A second down conversionreduces the signal to baseband. The QPSK signal 55 a, 55 b is thenfiltered 53 and mixed 56 with the locally generated complex pn sequence35I, 35Q which matches the conjugate of the transmitted complex code.Only the original signals which were spread by the same code will bedespread. All other signals will appear as noise to the receiver 21. Thedata 57 x, 57 y is coupled to a signal processor 59 where FEC decodingis performed on the convolutionally encoded data.

As shown in FIGS. 3A and 3B, a QPSK symbol consists of one bit each fromboth the in-phase (I) and quadrature (Q) signals. The bits may representa quantized version of an analog sample or digital data. It can be seenthat symbol duration t_(s) is equal to bit duration.

The transmitted symbols are spread by multiplying the QPSK symbol streamby the complex pn sequence. Both the I and Q pn sequences are comprisedof a bit stream generated at a much higher frequency, typically 100 to200 times the symbol rate. One such pn sequence is shown in FIG. 3C. Thecomplex pn sequence is mixed with the symbol bit stream producing thedigital spread signal (as previously discussed). The components of thespread signal are known as chips having a much smaller duration t_(c).

When the signal is received and demodulated, the baseband signal is atthe chip level. When the I and Q components of the signal are despreadusing the conjugate of the pn sequence used during spreading, the signalreturns to the symbol level.

The embodiments of the present invention are shown in FIGS. 4, 5 and 7.The global pilot signal cancellation system 61 embodiment is shown inFIG. 4. A received signal r is expressed as:r=∝c _(p) +βc _(t) +n  Equation (2)where the received signal r is a complex number and is comprised of thepilot strength ∝ multiplied with the pilot code c_(p), summed with thetraffic strength β multiplied with the traffic code c_(t), summed withrandom noise n. The noise n includes all received noise and interferenceincluding all other traffic signals. To cancel the global pilot signalfrom the received signal r, the system 61 must derive the signalstrength of the pilot code ∝ where:∝≠β  Equation (3)since the global pilot is transmitted at a higher power level than atraffic signal.

When the received signal r is summed over time, Equation (2) becomes:Σr=∝Σc _(p) +βΣc _(t) +Σn.  (Equation 4)

Referring to FIG. 4, the received baseband signal r is input 63 into thepilot signal cancellation system 61 and into a pilot despreader 65 whichdespreads the pilot signal from the received signal r. First mixer 67despreads the received signal r by multiplying with the complexconjugate c_(p)* 69 of the pilot pn code used during spreading yielding:Σrc* _(p) =∝c _(p) c* _(p) +βΣc _(t) c* _(p) +Σnc* _(p).  Equation (5)A complex conjugate is one of a pair of complex numbers with identicalreal parts and with imaginary parts differing only in sign.

The despread pilot signal 71 is coupled to a first sum and dumpprocessor 73 where it is summed over time. The first sum and dump 73output O_(sd1) is:O _(sd1) =∝L+βΣc _(t) c* _(p) +Σnc* _(p)  Equation (6)where L is the product of the pilot spreading code c_(p) and the complexconjugate of the pilot spreading code c_(p)* summed over L chips.

The sum and dump 73 output O_(sd1) is coupled to a low pass filter 75.The low pass filter 75 determines the mean value for each signalcomponent. The mean value for pilot-traffic cross-correlation is zeroand so is the mean value of the noise n. Therefore, after filtering 75,the second and third terms in Equation (6) become zero. The low passfilter 75 output O_(lpf) over time is:O _(lbf) =∝L  Equation (7)

The low pass filter 75 output O_(lpf) is coupled to a processing means77 to derive the pilot code strength ∝. The processing means 77calculates ∝ by dividing the low pass filter 79 output O_(lpf) by L.Thus, the processing means 77 output O_(pm) is:O _(pm)=∝.  Equation (8)

The pilot spreading code c_(p)* complex conjugate generator 69 iscoupled to a complex conjugate processor 79 yielding the pilot spreadingcode c_(p). The pilot spreading code c_(p) is input to a second mixer 81and mixed with the output of a traffic spreading code c_(t)* complexconjugate generator 83. The resulting product from the second mixer 81output is coupled to a second sum and dump processor 85. The outputO_(sd2) of the second sum and dump processor 85 is Γc_(p)c_(t)* and iscombined with at a third mixer 87. The third mixer 87 output 89 is∝Γc_(p)c_(t)*.

The received signal r is also despread by traffic despreader 91. Thetraffic despreader 91 despreads the received signal r by mixing thereceived signal r with the traffic code c_(t)* complex conjugategenerator 83 using a fourth mixer 93 yielding:Σrc* _(t) =∝Σc _(p) c* _(t) +βΣc _(t) c* _(t) +Σnc* _(t).  Equation (9)The traffic despreader 91 output 95 is coupled to a third sum and dump97. The third sum and dump 97 output O_(sd3) over time is:O _(sd3) =Σrc _(t) =βL+∝Σc _(p) c* _(t) +Σnc* _(t)  Equation (10)where L is the product of the traffic spreading code c_(t) and thecomplex conjugate of the traffic spreading code c_(t)* summed over Lchips.

The third sum and dump 97 output O_(sd3) is coupled to an adder 99 whichsubtracts the third mixer 87 output 89. The adder 99 output O_(add) is:O _(add) =βL+∝Σc _(p) c* _(t) +Σnc* _(t) −∝Σc _(p) c* _(t).  Equation(11)

Thus, the pilot canceller 61 output O_(add) is equal to the receivedsignal r minus the pilot signal simplified below:O _(add) =βL+Σnd* _(t).  Equation (12)

The invention uses a similar approach to cancel unwanted trafficsignal(s) from a desired traffic signal. While traffic signals areinterference to other traffic signals just as the global pilot signalis, unwanted traffic signal cancellation differs from global pilotsignal cancellation since a traffic signal is modulated by the data andis therefore dynamic in nature. A global pilot signal has a constantphase, whereas a traffic signal constantly changes phase due to datamodulation.

The traffic signal canceller system 101 embodiment is shown in FIG. 5.As above, a received signal r is input 103 to the system:r=ψdc _(d) +βc _(t) +n  Equation (13)where the received signal r is a complex number and is comprised of thetraffic code signal strength Θ multiplied with the traffic signal data dand the traffic code c_(d) for the unwanted traffic signal to becanceled, summed with the desired traffic code strength β multipliedwith the desired traffic code c_(t), summed with noise n. The noise nincludes all received noise and interference including all other trafficsignals and the global pilot signal. To cancel the unwanted trafficsignal(s) from the received signal r, the system 101 must derive thesignal strength of the unwanted traffic code Θ to be subtracted andestimate the data d, where:ψ≠d≠β.  Equation (14)

When the received signal r is summed over time, Equation 13 can beexpressed as:Σr=ψdΣc _(d) +βΣc _(t) +Σn.  Equation (15)

Referring to FIG. 5, the received baseband signal r is input 103 intothe desired traffic signal despreader 91 which despreads the desiredtraffic signal from the received signal r. Desired traffic signal mixer93 mixes the received signal r with the complex conjugate c_(t)* of thedesired traffic pn code used during spreading. The despread trafficsignal is coupled to a sum and dump processor 97 and summed over time.The sum and dump 97 output O_(sd3) is:O _(sd3) =Σrc* _(t) =βL+ψdΣc _(d) c* _(t) +Σnc* _(t).  Equation (16)

The traffic signal canceller system 101 shown in FIG. 5 includes nunwanted traffic signal cancellers 115 ₁-115 _(n). An exemplaryembodiment includes 10 (where n=10) unwanted traffic signal cancellers115 ₁-115 ₁₀.

Each unwanted traffic signal canceller 115 ₁-115 _(n) comprises: anunwanted traffic signal despreader 139 ₁-139 _(n) that includes a firstmixer 117 ₁-117 _(n) and an unwanted traffic signal code generator 119₁-119 _(n); second 133 ₁-133 _(n) mixer, first 121 ₁-121 _(n) and second123 ₁-123 _(n) sum and dump processors, a hard decision processor 125₁-125 _(n), a low pass filter 127 ₁-127 _(n), a processing means 129₁-129 _(n), third mixer 131 ₁-131 _(n), a conjugate processor 135 ₁-135_(n), an adjustable amplifier 137 ₁-137 _(n), and a desired trafficsignal code generator 83.

As above, the received signal r is input 103 into each unwanted trafficcanceller 115 ₁-115 _(n). The unwanted traffic signal despreader 139₁-139 _(n) is coupled to the input 103 where the received signal r ismixed 117 ₁-117 _(n) with the complex conjugate c_(d1)*-c_(dn)* of thetraffic pn sequence for each respective unwanted signal. The despread139 ₁-139 _(n) traffic signal is coupled to a first sum and dumpprocessor 121 ₁-121 _(n) where it is summed over time. The first sum anddump 121 ₁-121 _(n) output O_(sd1n) is:O _(sd1n) =Σrc* _(dn) =ψdL+βΣc _(t) c* _(dn) +Σnc* _(dn).  Equation (17)where L is the product of the unwanted traffic signal spreading codec_(dn) and c_(dn)* is the complex conjugate of the unwanted trafficsignal spreading code.

The first sum and dump 121 ₁-121 _(n) output O_(sd1n) is coupled to thehard decision processor 125 ₁-125 _(n). The hard decision processor 125₁-125 _(n) determines the phase shift Ø in the data due to modulation.The hard decision processor 125 ₁-125 _(n) also determines the QPSKconstellation position d that is closest to the despread symbol value.

As shown in FIG. 6, the hard decision processor 125 ₁-125 _(n) comparesa received symbol p_(o) of a signal to the four QPSK constellationpoints x_(1,1), x_(−1,1), x_(−1,−1), x_(1,−1). It is necessary toexamine each received symbol p_(o) due to corruption during transmission47 by noise and distortion, whether multipath or radio frequency. Thehard decision processor computes the four distances d₁, d₂, d₃, d₄ toeach quadrant from the received symbol p_(o) and chooses the shortestdistance d₂ and assigns that symbol d location x_(−1,1). The harddecision processor also derotates (rotates back) the original signalcoordinate p_(o) by a phase amount Ø that is equal to the phasecorresponding to the selected symbol location x_(−1,1). The originalsymbol coordinate p_(o) is discarded.

The hard decision processor 125 ₁-125 _(n) phase output Ø is coupled toa low pass filter 127 ₁-127 _(n). Over time, the low pass filter 127₁-127 _(n) determines the mean value for each signal component. The meanvalue of the traffic-to-traffic cross-correlation and also the meanvalue of the noise n are zero. Therefore, the low pass filter 127 ₁-127_(n) output O_(lpfn) over time is:O _(lpfn) =ψL.  Equation (18)

The low pass filter 127 ₁-127 _(n) output O_(lpfn) is coupled to theprocessing means 129 ₁-129 _(n) to derive the unwanted traffic signalcode strength Θ. The processing means 129 ₁-129 _(n) estimates Ø bydividing the filter 127 ₁-127 _(n) output O_(lpfn) by L.

The other hard decision processor 125 ₁-125 _(n) output is data d. Thisis the data point d corresponding to the smallest of the distances d₁,d₂, d₃, or d₄ as shown in FIG. 6. Third mixer 131 ₁-131 _(n) mixes theunwanted traffic signal strength Θ with each data value d.

The unwanted traffic signal spreading code complex conjugate generatorc_(d1)*-c_(dn)* is coupled to the complex conjugate processor 135 ₁-135_(n) yielding the unwanted traffic signal spreading code c_(d1)-c_(dn)and is input to the second mixer 133 ₁-133 _(n) and mixed with theoutput of desired traffic signal spreading code complex conjugategenerator c_(t)*. The product is coupled to the second sum and dumpprocessor 123 ₁-123 _(n). The second sum and dump processor 123 ₁-123_(n) output O_(sd2n) is Γcd_(n)c_(t)* and is coupled to variableamplifier 137 ₁-137 _(n). Variable amplifier 137 ₁-137 _(n) amplifiesthe second sum and dump processor 123 ₁-123 _(n) output O_(sd2n) inaccordance with the third mixer 131 ₁-131 _(n) output which is thedetermined gain.

The variable amplifier 137 ₁-137 _(n) output 141 ₁-141 _(n) is coupledto an adder 143 which subtracts the output from each variable amplifier137 ₁-137 _(n) from the output of the desired traffic signal despreader115. The output O is:O=βL+ψdΣc _(d) c* _(t) +Σnc* _(t) −ψdΣc _(d) c* _(t).  Equation (19)The adder 143 output O (also the unwanted traffic canceller system 101output) is equal to the received signal r minus the unwanted trafficsignals simplified below:O=βL+Σnc* _(t)  Equation (20)where the noise n varies depending on the amount of traffic signalssubtracted from the received signal.

Another embodiment 145 canceling the global pilot signal and unwantedtraffic signals is shown in FIG. 7. As previously discussed, theunwanted traffic cancellation system 101 includes the desired trafficsignal despreader 91 and a plurality of unwanted traffic signalcancellers 115 ₁-115 _(n). The traffic cancellation system is coupled inparallel with the pilot cancellation system 61 previously described, butwithout a desired traffic signal despreader. A common input 147 iscoupled to both systems 101, 61 with a common adder 149 which is coupledto the outputs O, O_(add) from both systems 101, 61. The pilot andunwanted traffic signals are subtracted from the desired traffic signalyielding an output 151 free of interference contributions by the pilotand plurality of transmitted traffic signals.

While specific embodiments of the present invention have been shown anddescribed, many modifications and variations could be made by oneskilled in the art without departing from the spirit and scope of theinvention. The above description serves to illustrate and not limit theparticular form in any way.

1. A method for removing a selected signal from a received signal, themethod comprising: receiving code division multiple access (CDMA)signals including a first signal and a second signal, the first signalbeing spread with a first spreading code and the second signal beingspread with a second spreading code; despreading the received CDMAsignals with a complex conjugate of the first spreading code to generatea first de-spread signal; despreading the received CDMA signals with acomplex conjugate of the second spreading code to generate a secondde-spread signal; generating a symbol value based on the secondde-spread signal; generating a second signal strength based on thesecond de-spread signal; calculating a correlation of the secondspreading code and a complex conjugate of the first spreading code;generating a cancellation signal component based on the correlation, thesecond signal strength, and the symbol value; and subtracting thecancellation signal component from the first de-spread signal.
 2. Themethod of claim 1 wherein the second signal strength is generated by:generating a phase error between the symbol value and the secondde-spread signal in a constellation; derotating the second de-spreadsignal by the phase error; low-pass-filtering the derotated secondde-spread signal; and dividing a low-pass-filtered value by a product ofthe second spreading code and the complex conjugate of the secondspreading code.
 3. The method of claim 1 further comprising: despreadingthe received CDMA signals with a complex conjugate of a pilot spreadingcode to generate a third de-spread signal; generating a pilot signalstrength based on the third de-spread signal; calculating a secondcorrelation of the pilot spreading code and a complex conjugate of thefirst spreading code; generating a second cancellation signal componentbased on the second correlation and the pilot signal strength; andsubtracting the second cancellation signal component from the firstde-spread signal.
 4. The method of claim 3 wherein the pilot signalstrength is generated by: low-pass-filtering the third de-spread signal;and dividing the low-pass-filtered third de-spread signal with a productof the pilot spreading code and a complex conjugate of the firstspreading code.
 5. A method for removing the pilot signal from areceived signal, the method comprising: receiving code division multipleaccess (CDMA) signals including a first signal and a pilot signal, thefirst signal being spread with a first spreading code and the pilotsignal being spread with a pilot spreading code; despreading thereceived CDMA signals with a complex conjugate of the first spreadingcode to generate a first de-spread signal; despreading the received CDMAsignals with a complex conjugate of the pilot spreading code to generatea second de-spread signal; generating a pilot signal strength based onthe second de-spread signal; calculating a correlation of the pilotspreading code and a complex conjugate of the first spreading code;generating a pilot cancellation signal component based on thecorrelation and the pilot signal strength; and subtracting the pilotcancellation signal component from the first de-spread signal.
 6. Themethod of claim 5 wherein the pilot signal strength is generated by:low-pass-filtering the second de-spread signal; and dividing thelow-pass-filtered second de-spread signal with a product of the pilotspreading code and a complex conjugate of the first spreading code. 7.An apparatus configured to remove a selected signal from a receivedsignal, the apparatus comprising: a receiver for receiving code divisionmultiple access (CDMA) signals including a first signal and a secondsignal, the first signal being spread with a first spreading code andthe second signal being spread with a second spreading code; a firstdespreader for despreading the received CDMA signals with a complexconjugate of the first spreading code to generate a first de-spreadsignal; a second despreader for despreading the received CDMA signalswith a complex conjugate of the second spreading code to generate asecond de-spread signal; a hard decision processor for generating asymbol value based on the second de-spread signal; a signal strengthgeneration device for generating a second signal strength based on thesecond de-spread signal; a correlator for calculating a correlation ofthe second spreading code and a complex conjugate of the first spreadingcode; a cancellation signal generation device for generating acancellation signal component based on the correlation, the secondsignal strength, and the symbol value; and a subtractor for subtractingthe cancellation signal component from the first de-spread signal. 8.The apparatus of claim 7 wherein the signal strength generation devicecomprises: a hard decision processor for generating a phase errorbetween the symbol value and the second de-spread signal in aconstellation, and derotating the second de-spread signal by the phaseerror; a low-pass filter for low-pass-filtering the derotated secondde-spread signal; and a divider for dividing an output from thelow-pass-filter by a product of the second spreading code and thecomplex conjugate of the second spreading code.
 9. The apparatus ofclaim 7 further comprising: a third despreader for despreading thereceived CDMA signals with a complex conjugate of a pilot spreading codeto generate a third de-spread signal; a pilot signal strength generatorfor generating a pilot signal strength based on the third de-spreadsignal; a second correlator for calculating a second correlation of thepilot spreading code and a complex conjugate of the first spreadingcode; and a second cancellation signal generator for generating a secondcancellation signal component based on the second correlation and thepilot signal strength, wherein the subtractor subtracts the secondcancellation signal component from the first de-spread signal.
 10. Theapparatus of claim 9 wherein the pilot signal strength generatorcomprises: a low-pass filter for low-pass-filtering the third de-spreadsignal; and a divider for dividing an output from the low-pass-filterwith a product of the pilot spreading code and a complex conjugate ofthe first spreading code.
 11. An apparatus for removing the pilot signalfrom a received signal, the method comprising: a receiver for receivingcode division multiple access (CDMA) signals including a first signaland a pilot signal, the first signal being spread with a first spreadingcode and the pilot signal being spread with a pilot spreading code; afirst despreader for despreading the received CDMA signals with acomplex conjugate of the first spreading code to generate a firstde-spread signal; a second despreader for despreading the received CDMAsignals with a complex conjugate of the pilot spreading code to generatea second de-spread signal; a pilot signal strength generator forgenerating a pilot signal strength based on the second de-spread signal;a correlator for calculating a correlation of the pilot spreading codeand a complex conjugate of the first spreading code; a cancellationsignal generator for generating a pilot cancellation signal componentbased on the correlation and the pilot signal strength; and a subtractorfor subtracting the pilot cancellation signal component from the firstde-spread signal.
 12. The apparatus of claim 11 wherein the pilot signalstrength generator comprises: a low-pass filter for low-pass-filteringthe second de-spread signal; and a divider for dividing an output fromthe low-pass-filter with a product of the pilot spreading code and acomplex conjugate of the first spreading code.